Titanium in metallic form or as a compound is an important element in the chemical series. For example, titanium dioxide is utilized in paint pigments, in white rubbers and plastics, floor coverings, glassware and ceramics, painting inks, as an opacifying agent in papers, etc. The other titanium compounds are used in electronics, as fire retardants, waterproofing agents, etc. The metal may be used as such or in alloy form as structural material in aircraft, in jet engines, marine equipment, textile machinery, surgical instruments, orthopedic appliances, sporting equipment, food handling equipment, etc. Heretofore in recovering the titanium from titanium bearing sources such as ilmenite, rutile, etc., the titanium has been subjected to separation steps which involve the formation of titanium as a compound in a valence state of +4, such compounds usually involving titanium oxide. However, when attempting to separate titanium dioxide from impurities which are also contained in the ore such as iron, the hydrolysis of the titanium dioxide at elevated temperatures usually results in also obtaining relatively large amounts of iron along with the titanium.
Heretofore in the prior art various methods have been utilized to recover titanium values from titanium bearing sources. For example, in U.S. Pat. No. 3,236,596 an unroasted ilmenite ore is leached with hydrogen chloride at an elevated temperature. Following this, dissolved iron is reduced with iron or other reductants to precipitate ferrous chloride by saturating the liquor with hydrogen chloride gas. The hydrogen chloride is then extracted from the liquor by a vacuum distillation and the titanium is recovered by conventional means. Likewise, U.S. Pat. No. 3,825,419 reduces an ilmenite ore to produce ferrous oxides. The reduced ore is then leached for about 4 hours under a moderate pressure thereby dissolving the iron in the acid along with about 15% of the titanium. The iron is recovered as ferric oxide containing impurities in the spray roaster while the insoluble product which is primarily titanium dioxide but which contains all of the silica present in the original ore is recovered. U.S. Pat. No. 3,859,077 also discloses a process for recovering titanium in which a titanium tetrahalide is mixed with iron oxide in slag or a titaniferous ore at an extremely high temperature of about 1000.degree. C. to produce volatile impurity chlorides and titanium dioxide. A similar patent, U.S. Pat. No. 3,929,962, also reduces a titanium bearing ore at a high temperature to produce titanium sesquioxide which is in a form whereby it is easier to treat for a titanium-iron separation. Another prior art reference, U.S. Pat. No. 3,903,239 teaches a method for recovering titanium in which unroasted ilmenite is leached over a period of days at room temperature to recover about 80% of the titanium. Sulfur dioxide is added during the leaching to cause a precipitation of the ferrous chloride after which titanium dioxide is recovered by diluting and heating the solution.
In contradistinction to these prior art methods of recovering titanium values from a titanium bearing source, I have now found that it is possible to produce a titanium dioxide by reaction with ferric oxide whereby the process will possess several advantages over the present technology. These advantages will hereinafter be set forth in greater detail.
This invention relates to a process for obtaining titanium metal values from a titanium bearing source. More specifically the invention is concerned with a process for recovering titanium from a titanium bearing source such as ilmenite whereby a greater amount of titanium is obtained from the separation. The advantages of utilizing the process of the present invention are found in the fact that the reactions are effected in a relatively short period of time, for example, the leaching of the titanium ore which has been reduced can be effected during a period of from about 0.25 to about 0.5 hours and the precipitation of the desired titanium dioxide may be effected in a period as low as 0.1 hour. In addition, another advantage which is present when utilizing the process of the present invention is that the reactions may, if so desired, be effected at atmospheric pressure thus obviating the use of relatively expensive and complicated equipment. In addition to the aforesaid advantages, it is possible to obtain a desired yield of titanium metal values using relatively low grade ores as the starting material. Other advantages which are present in the present process are that the leach solution possesses an excellent stability at relatively high temperatures due to the high reducing potential of the solutions which are employed; the recovery of the titanium dioxide as rutile is effected at temperatures less than the boiling point of the solution with a high purity of the desired product; the acid need not be diluted to precipitate the titanium dioxide, thus decreasing the demand for water.
It is therefore an object of this invention to provide an improved process for the production of titanium metal values.
A further object of this invention is to provide a hydrometallurgical process for obtaining high yields of titanium metal values from titanium bearing sources.
In one aspect an embodiment of this invention resides in a process for the recovery of titanium values from a titanium bearing source which comprises subjecting said titanium bearing source to a reductive roast, thereafter leaching the reduced source with a hydrogen chloride source in a leaching zone, precipitating the leached titanium bearing source in a precipitation zone by contact with a metal oxide in which the metal is present in a highly oxidized state, separating and recovering the resultant precipitated titanium dioxide, treating the spent liquor to form and recycle hydrogen chloride to said leaching zone, and simultaneously forming the metal oxide for recycle to said precipitation zone.
A specific embodiment of this invention is found in a process for the recovery of titanium values from a titanium bearing source such as ilmenite which comprises subjecting said ilmenite to a reductive roast at a temperature in the range of from about 650.degree. to about 1000.degree. C., thereafter leaching the reduced source with hydrochloric acid in a leaching zone at a temperature in the range of from about 85.degree. to about 105.degree. C., precipitating the leached titanium bearing source in a precipitation zone by contact with ferric oxide at a temperature in the range of from about 75.degree. to about 105.degree. C., separating and recovering the resultant precipitated titanium dioxide, treating the spent liquor to form and recycle hydrochloric acid to said leaching zone and simultaneously forming ferric oxide for recycle to said precipitation zone.
Other objects and embodiments will be found in the following further detailed description of the present invention.
As hereinbefore set forth the present invention is concerned with an improved process for obtaining titanium metal values from a titanium bearing source such as ores including ilmenite, rutile, etc. By utilizing the present process it is possible to obtain a high yield of the desired product while utilizing relatively inexpensive equipment and also starting with a low grade ore. The process is effected by subjecting a titanium bearing source which also contains other metals, preferably iron, as well as vanadium, chromium, manganese, etc., to a reductive roast at an elevated temperature which will range from about 650.degree. to about 1000.degree. C. or more, said reductive roast being effected in the presence of a reductant such as hydrogen, carbon monoxide, combination of carbon monoxide and hydrogen, etc., or any other suitable reductant. In the preferred embodiment, the reductive roast is effected on a metal bearing source such as an ore which has been crushed to a particle size less than about 100 mesh for a period of time ranging from about 0.5 up to about 2 hours or more. In the preferred embodiment of the invention the reducing atmosphere which is used to accomplish the purpose of the roast usually comprises a mixture of about 50% carbon monoxide and 50% hydrogen with an excess of the reductant being utilized in order to completely reduce the iron which is present in the system to the metal. Following the reductive roast of the metal bearing source, the source is then subjected to an aqueous hydrogen chloride leach which is also effected at elevated temperatures usually in the range of from about 85.degree. to about 105.degree. C. for a period of time ranging from about 0.25 up to about 1 hour or more in duration. The aqueous hydrogen chloride solution which may also be characterized as hydrochloric acid will contain from about 20% up to about 37% hydrogen chloride. Upon completion of the leach step, the leached solution is thereafter treated with a metal oxide in which the metal portion of the oxide is present in a highly oxidized state. Some examples of these metal oxides which may be used to precipitate the titanium will include ferric oxide, vanadium pentoxide, vanadium dioxide, chromic oxide, manganese dioxide, cupric oxide, etc. The precipitated titanium dioxide is thereafter separated from the spent liquor and recovered while the aforesaid spent liquor is then treated to simultaneously form hydrogen chloride which is recycled to the leaching zone and the metal oxide which may then be recycled to the precipitation zone or recovered. In the preferred embodiment of the invention the metal oxide may be recycled to the precipitation zone in an amount ranging from about 50% to about 100% by weight of the titanium bearing source, the remainder being recovered for subsequent sale as metal oxide. In the preferred embodiment of the invention the treatment of the spent liquor is effected in a spray drying apparatus wherein the liquor is heated to a temperature ranging from about 300.degree. up to about 950.degree. C. in an oxidizing atmosphere provided for by either air, oxygen or a mixture of air and oxygen.